Notizenseiten zum Seminarvortrag: High-frequency electromagnetic scattering by non-metallic wedges

Kurzfassung

This report is based on viewgraphs and notes of a talk given at a seminar of the DLR Microwave and Radar Institute, Oberpfaffenhofen, on December 10, 2002. The talk has summarized an approach developed in Radar Signatures Laboratory throughout the last three years to simulate high-frequency electromagnetic scattering from edges of non-metallic faceted targets. The approach is based on the following four observations. (1) Contributions from edges may play an important role. (2) The key quantity for theoretical analysis is the GTD diffraction coefficient. If this is known, one can easily calculate edge contributions/corrections in both Fresnel (mobile radio case) and Fraunhofer (RCS applications) zones. A uniform diffraction coefficient is simply expressed through the GTD diffraction coefficient. (3) Though exact numerical specification of the diffraction coefficient is possible, an implementation of the exact solution into simulation procedures appears to be too time-consuming. (4) A more practical approach is to develop a justified approximation to the diffraction coefficient. In that case, the exact solution is employed as a reference to estimate accuracy of the approximation. The construction of the approximate diffraction coefficient consists of two steps, which are the use of approximate boundary conditions (for example, impedance) followed by an approximate treatment of the corresponding boundary-value problem. For the particular case of an external impedance wedge, such an approximate diffraction coefficient has been obtained and is presented in the report. The derived analytical expression is extremely simple, including only elementary functions and Fresnel reflection coefficients. It is exact in the limiting cases of PEC half- and full-planes. For a more general wedge angle and/or a finite value of the surface impedance, it is an approximation. We have conducted extensive studies of the approach, proving its being adequate for both Fresnel and Fraunhofer’s zones. The obtained solution can be easily implemented into microwave propagation and scattering simulation software, including the RCS prediction tools SIGMA and BISTRO being developed in the Radar Signatures Laboratory. We believe that the approach can be extended to other wedge configurations, like internal wedges and wedge-shaped junctions of thin impedance sheets.